The invention relates to a method for determining the angle of anteversion and/or the angle of inclination of an acetabulum in a pelvic bone.
When implanting an acetabulum, which generally has as an approximately hemispherical shape, the position of the acetabulum and its angular position relative to the pelvic bone must be precisely determined before the implantation. The position can be determined relatively easily by the center point of rotation of the hip joint being determined prior to the implantation, for example, by pivoting the femur relative to the pelvic bone. This center point then corresponds to the spherical center point of the hemispherical acetabulum.
The determination of the angular position of the acetabulum proves more difficult. The acetabulum has a bottom rim which defines a plane delimiting the hemispherical acetabulum at the bottom end, and there extends perpendicularly to this plane a central axis of the hemispherical acetabulum, which passes through the center point of the acetabulum. This central axis of the acetabulum is generally arranged in space such that it includes different angles with the main planes of the pelvic bone. Main planes of the pelvic bone are to be understood as the transverse plane, i.e., a plane extending horizontally in an upright pelvis, the sagittal plane, i.e., a plane running from front to back and extending perpendicularly to the transverse plane in an upright pelvis, and the frontal plane which extends perpendicularly to the two aforementioned planes.
To describe the position of the central axis relative to these main planes, it is standard practice to indicate the angle of anteversion and the angle of inclination. The angle of anteversion describes the angle which an anteversion plane containing the central axis and extending perpendicularly to the transverse plane includes with a frontal plane. The angle of inclination describes the angle which an inclination plane extending perpendicularly to the central axis of the acetabulum and extending perpendicularly to a frontal plane assumes relative to a sagittal plane.
In practice, the angle of anteversion and the angle of inclination are determined by complicated preliminary examinations carried out on the patient, for example, by X-rays taken in various planes or by ultrasonic examinations, which involve a great deal of expenditure, and, in particular, in the case of X-ray examinations, expose the patient to a high dose of radiation.